BeechTalk - BT - Phenom 300 advised not to fly during GPS shutdown

Username Protected · **Posted:** 07 Jun 2016, 15:34

Just ran into this NOTAM, related to a GPS shutdown test sometime today

ADDITIONALLY, DUE TO GPS INTERFERENCE IMPACTS POTENTIALLY AFFECTING EMBRAER PHENOM 300 ACRAFT FLIGHT STABILITY CONTROLS, FAA RECOMMENDS EMB PHENOM PILOTS AVOID THE ABV TESTING AREA AND CLOSELY MONITOR FLIGHT CONTROL SYSTEMS DUE TO POTENTIAL LOSS OF GPS SIGNAL. 1606081830-1606082000

Just curious, why is the Phenom 300 more impacted than others?

Username Protected · **Posted:** 07 Jun 2016, 16:18

http://www.faa.gov/documentLibrary/media/Notice/GENOT_7110_711_EMB-300.pdf

Username Protected · **Posted:** 07 Jun 2016, 16:23

Holy Crap

Glad we are in Cessnas!

Username Protected · **Posted:** 07 Jun 2016, 16:26

Username Protected · **Posted:** 07 Jun 2016, 16:27

I'll find out.
We operate one.

Username Protected · **Posted:** 07 Jun 2016, 16:41

Based on what little I know about the Phenom 300, that ventral fin is a SIGNIFICANT flight control surface that corrects a number of flight conditions beyond simple yaw. The 100 does not have it and if you see one in person on a 300 or look closely, the fin is hinged.

It's the only plane I can think of that has an active ventral fin AND a GPS-augmented AHARS-based FCS. Anything higher in the food chain is going to have INS, I would think.

I wonder what the fix would be for a nine-million dollar aircraft that shouldn't be flying without strong GPS for flight control purposes...

Username Protected · **Posted:** 07 Jun 2016, 20:35

Wow they fubared that design. Didn't they hear about 9/11.

Username Protected · **Posted:** 07 Jun 2016, 20:58

That settles it. I was going to put a deposit down on a Phenom 300 tomorrow, but now I am going to stick with my flying museum piece.

Username Protected · **Posted:** 07 Jun 2016, 21:44

Username Protected wrote:

Based on what little I know about the Phenom 300, that ventral fin is a SIGNIFICANT flight control surface that corrects a number of flight conditions beyond simple yaw. The 100 does not have it and if you see one in person on a 300 or look closely, the fin is hinged.

It's the only plane I can think of that has an active ventral fin AND a GPS-augmented AHARS-based FCS. Anything higher in the food chain is going to have INS, I would think.

I wonder what the fix would be for a nine-million dollar aircraft that shouldn't be flying without strong GPS for flight control purposes...

How'd this ever get off the design table?

Username Protected · **Posted:** 07 Jun 2016, 21:50

I am sure Embraer is more surprised than anybody and working on a fix.

Username Protected · **Posted:** 07 Jun 2016, 22:00

Username Protected wrote:

It's the only plane I can think of that has an active ventral fin AND a GPS-augmented AHARS-based FCS. Anything higher in the food chain is going to have INS, I would think.

..

Lots of jets higher on the food chain don't have inertials.

I'm sure the 300 wouldn't spin out of control with a loss of GPS...it's probably just one of those can't fly into a known outage things ( more legal than technical), since attitude has a GPS component in the Kalman filter- my guess

Username Protected · **Posted:** 07 Jun 2016, 22:28

I'm sure the plane flies fine without GPS... it's the pilots they are concerned about...

Username Protected · **Posted:** 07 Jun 2016, 22:30

Poor design for the flight control system to be that dependent on GPS signal.

Username Protected · **Posted:** 07 Jun 2016, 23:34

could that "snag" reveal a systemic design problem with Garmin AHRS systems?

seems as if that AHRS has gotten too much of the Garmin GPS treatment…

an AHRS should not need GPS to work properly..as a source for aircraft systems, i.e. yaw dampers and others, GPS should not be allowed to interfere with AHRS output..or AHRS output should not be dependent on GPS...

just asking..?

that sounds like a potential major problem to me….(and not "just" in regards to that Phenom 300's flight control system…), but in general…

Username Protected · **Posted:** 08 Jun 2016, 00:01

Username Protected wrote:

GPS should not be allowed to interfere with AHRS output..

An "integrated" system in one in which no single human understands all the possible interactions.

Here we have an AHRS apparently using GPS for verification/operation, and they tapped yaw rate for the yaw damper, not realizing that is dependent on GPS. No GPS, no yaw damp, instability for a swept wing airplane, emergency descent.

Just remember this lesson for all you out there that want a fully electronic panel. Does anyone really understand all the possible failure modes?

There will always be at least one spinning chunk of metal in my panel for this reason.

Mike C.